UV damage and sun care: deciphering mechanics of skin to develop next generation therapies

The Whitening Properties of the Mixture Composed of Pomegranate, Osmanthus and Olive and the Protective Effects Against Ultraviolet Deleterious Effects

Background

Ultraviolet (UV) rays are the major environmental factor that damage skin physiology causing deleterious effects such as oxidation, photoaging and pigmentation. There has been considerable interest in using botanicals to prevent skin damages caused by UV irradiation.

Aim

In this study, three plant extracts were tested either individually or combined together (mixture) as well as their corresponding main active compound: pomegranate/punicalagin, osmanthus/verbascoside and olive/hydroxytyrosol. We evaluated the whitening and anti-photoaging properties of the nutritional mixture using 2D human culture model and a 3D full-thickness pigmented skin model exposed to UVB and UVA.

Methods

For exploring skin pigmentation, oxidation and aging, we performed cell viability, tyrosinase activity and melanin content assays as well as histology analysis (Whartin–Starry staining), immunodetection (PMEL, MDA, collagen type I and elastin) and carbonylated proteins analysis by electrophoresis separation.

Results

Results showed that the pomegranate extract and the active molecule punicalagin could reduce the tyrosinase activity and melanin content in melanocytes (P < 0.05). The mixture, pomegranate extract and punicalagin inhibited the melanin production and pre-melanosomal protein (PMEL) expression in the 3D skin pigmented model (P < 0.001). Furthermore, the mixture treatment repaired the expressions of collagen I and elastin decrease by UV exposure (P < 0.01). The mixture also significantly decreased lipid peroxidation (P < 0.001) and carbonylated proteins (P < 0.05) in the skin model compared to the UV-exposed condition.

Conclusion

To conclude, the mixture composed of pomegranate, osmanthus and olive extracts protects human skin from UV rays deleterious effects and exhibits antioxidative, anti-aging and skin whitening properties. Our data suggested pomegranate contributed to the whitening properties of the mixture notably through its main active compound, punicalagin. The mixture might be a good candidates for further development as natural antioxidant and skin care product.

Maximum tensile stress and strain of skin of the domestic pig-differences concerning pigs from organic and non-organic farming

The purpose of this work has been to determine differences in biomechanical properties of porcine skin from organic and non-organic farming as porcine skin is widely used as a model for human skin. A test apparatus was used, using gravity to stretch and finally tear a dumbbell-shaped specimen of prepared abdominal skin with a testing surface area of 25 × 4 mm. A total of 32 specimens were taken from seven individual pigs, three from organic and four from non-organic farming, in different orientations with respect to the Langer's lines. The tests were performed at a dynamic speed of around 1.66 m/s (corresponding to a nominal strain rate of 67 s^-1). Engineering strain at rupture was higher in pig skin from non-organic farming with values up to 321% as opposed to 90% in organic pig skin. The maximum tensile stress found in non-organic pig skin was lower than in pig skin from organic farming with maximum values of 34 MPa as opposed to 58 MPa. The reason for the difference in biomechanical properties is unclear; the effect of sunlight is discussed as well as other factors like age and exercise. It seems that the biomechanical properties of porcine skin from organic farming are more similar to those of human skin.

Using ordered mesoporous silica SBA-15 to limit cutaneous penetration and transdermal permeation of organic UV filters

Avobenzone (AVO), oxybenzone (OXY), and octyl methoxycinnamate (OMC), are widely used UV filters. The aim of this study was to investigate the effect of incorporation in mesoporous silica (SBA-15) on their cutaneous deposition and permeation. Stick formulations containing "free" and "incorporated" UV filters (SF1 and SF2, respectively) were prepared and characterized with respect to their physicochemical, thermal, and functional properties. Cutaneous delivery experiments using porcine skin with quantification by UHPLC-MS/MS, demonstrated that skin deposition of AVO and OXY after application of SF2 for 6 and 12 h was significantly lower than that from SF1 at each time-point (Student t-test, p < 0.05): e.g. OXY permeation across the skin was 30-, 12- and 1.5-fold lower after 6, 12 and 24 h, respectively, following application of SF2. Cutaneous biodistribution profiles of AVO and OXY to 800 µm evidenced a significant decrease in the amounts in the viable epidermis and dermis. In contrast, deposition of the more lipophilic OMC was not significantly different (p ˃ 0.05). In vitro photoprotective efficacy results demonstrated that adsorption/entrapment of UV filters enhanced the sun protection factor by 94%. In conclusion, SBA-15, an innovative mesoporous material, increased photoprotection by UV filters while reducing their cutaneous penetration and transdermal permeation.

Ultrafast sonochemistry-based approach to coat TiO2 commercial particles for sunscreen formulation

TiO₂ is a common inorganic filter used in sunscreens due to its photoprotective effect on the skin against UV radiation. However, the use of this kind of material in cosmetics is limited by its inherent photocatalytic activity. It is known that coating on TiO₂ surface can improve some features. Although, many of the methodologies used for this purpose are still laborious and time-consuming. Thus, this work reports a novel, easy, cheap and fast strategy to coat TiO₂ particles by using a sonochemistry approach, aiming to decrease photocatalytic activity and to enhance colloidal stability. For this proposal, SiO₂, Al₂O₃, ZrO₂ and sodium polyacrylate (PAANa) were used to tune the surface of commercial TiO₂ particles and they were applied in a sunscreen formulation. The samples were characterized by XRPD, FT-IR, DLS, EDS, SEM and TEM. The photocatalytic activity and UV-shielding ability were also evaluated. The sunscreen formulations were prepared and characterized by zeta potential, DLS, and Sun Protection Factor (SPF). FT-IR, EDS, and charge surface of the particles confirmed the success of the sonochemistry coating. Additionally, TiO₂@Al₂O₃, TiO₂@SiO₂ and TiO₂@PAANa show a lower photocatalytic activity than original TiO₂ with similar UV-shielding ability. The sunscreens produced with the coated TiO₂ have similar SPF to the one with commercial TiO₂. Specifically, the sunscreen with TiO₂@PAANa shows an increase in colloidal stability. Herein, the incorporation of the sonochemical-coated TiO₂ particles in sunscreen formulations may produce sunscreens with better aesthetic appearance and a greater health security due to its lower free radicals production.